Just last August, Drew Barrymore was gushing over her close relationship with Cameron Diaz, calling her “the best friend anyone can ever have… it’s like she’s my big sister.”

The actresses, who bonded while shooting Charlie’s Angels in 2000, “did everything together,” a pal of Drew tells OK!.

So why, as <em>OK</em>! reported, did they avoid each other at the Jan. 11 Golden Globes CAA afterparty at L.A.’s Sunset Tower Hotel?

Drew and Cam “stayed on opposite sides of the room the entire night,” a guest told OK! at the time.

“At one point Drew breezed by Cameron and didn’t even glance at her. It was obvious they’re not best buds anymore,” said our source.

Perhaps they’ve grown apart?

Since Cameron’s father, Emilio, died last year, “she has become a more serious person,” her friend tells OK!.

“Drew can be silly and that’s just not where Cameron’s at.”

That extends to their love lives.

Drew, 33, has had flings with a slew of younger men, including Ed Westwick, 21, Fabrizio Morretti, 28, and Justin Long, 30, while Cameron, 36, has moved in with model — and Jennifer Aniston’s ex — Paul Sculfor, 37.

Drew’s friend tells OK!, “Now that Cameron and Paul have moved in together, Drew’s kind of a third wheel.”